Drip irrigation tape having a reduced thickness portion covering an indented flow groove

ABSTRACT

A drip irrigation tape is formed from a strip of flexible material having a series of spaced indented grooves of serpentine shape extending along one side edge, the strip being folded with its opposite side edges overlapping and sealed together on opposite sides of the grooves to form a main conduit within the folded strip and a series of secondary conduits along the grooves. Breaks in the seal form inlets between the main conduit and each secondary conduit, and raised outlet ports connect the secondary conduit to the exterior of the tape. The grooves each have a series of elongated chambers offset alternately on opposite sides of the grooved region and interconnected by orifices of smaller dimensions than the chambers.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 07/884,643, filedMay 21, 1992, now U.S. Pat. No. 5,246,171 which was acontinuation-in-part of application Ser. No. 07/712,201, filed Jun. 6,1991, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to drip irrigation tape and itsmanufacture.

Drip irrigation systems are commonly used in agriculture andhorticulture to conserve water and reduce costs. The drip irrigationsystem comprises lengths of plastic tubing or tape placed near the rootsof plants, either above ground or embedded in the earth, the tape havingnumerous small outlets supplying drops of water continuously to theplants. As well as conserving water, this arrangement provides a moreuniform water supply to plants, improving crops and reducing saltaccumulation and fertilizer loss in the soil.

Drip irrigation tape is commonly fabricated today from a thin pliableplastic strip folded lengthwise. The two edges are overlapped and joinedtogether to form a flat hollow tape that may be of the order of one inchwide. Under pressure, the tape opens out into a generally cylindricalform to provide the main conduit for irrigation water flowing to cropsor other plants under irrigation. The tape also includes a much smallersecondary conduit, usually located along the seam formed by theoverlapping side edges of the plastic strip, and connected to the mainconduit to form a narrower passageway to reduce the rate at which wateris emitted into the soil. The water trickles out of a series of outletsalong the secondary conduit. One problem in such tapes is to ensureuniform drip rate along the tape. This problem is particularly acute incases where extremely long runs of tape are to be used. Currently, themaximum run of tape which can be used from a water supply is around 600to 700 feet before a relatively large reduction in drip rate will beencountered. This can be a problem in large crop regions to beirrigated.

In my previous U.S. Pat. Nos. 4,722,759 and 4,807,668, a drip irrigationtape is described in which a strip of flexible material is formed withan indented groove extending lengthwise adjacent one side edge of thestrip, and the other side edge is folded over lengthwise to overlap thegroove and form the main conduit within the interior of the tape. Theoverlapping side edges are sealed together on opposite sides of thegroove to form a seam in which the groove forms a secondary conduit.Spaced inlets are provided between the main conduit and secondaryconduit, and spaced outlets lead from the secondary conduit to theexterior of the tape, so that fluid supplied to the main conduit flowsinto the secondary conduit and leaks slowly out of the outlets into thesurrounding soil.

In U.S. Pat. No. 4,722,759 a method of fabricating such tape isdescribed, in which a straight, continuous or segmented groove is formedalong the side edge of the strip on a vacuum drum. However, there issome advantage in providing a non-straight flow path along the secondaryconduit to create some turbulence in the fluid, tending to shift anydebris which might otherwise block the conduit. The tortuous or windingflow path will also reduce the flow rate and allow the dimensions of thesecondary conduit to be increased while providing the same drip rate asa corresponding straight conduit, further reduce the risk of debrisblocking the channel. Drip irrigation tape with a winding or serpentinesecondary conduit is described, for example, in U.S. Pat. No. 4,177,946of Sahagun-Barragan, U.S. Pat. No. 4,473,191 of Chapin, and in myco-pending application Ser. No. 07/485,778 filed Feb. 22, 1990,abandoned.

There are problems in manufacturing tape with a winding or serpentinesecondary conduit. In Sahagun-Barragan, the tape is formed from twosheets, one of which is embossed to form a winding channel. In Chapin,the winding channels are formed by a pair of paired ribbons of adhesiveor hot melt polymer between two flat sheets of plastic film, causingproblems in maintaining uniformity of the channel cross section alongits length. In my co-pending application Ser. No. 07/485,778, nowabandoned, referred to above, a method and apparatus for manufacturingirrigation tape with a winding secondary conduit is described, in whichopposing drums have mating indented groove and projecting mandrelformations for forming the channel, the shape of the mating groove andmandrel corresponding to the desired conduit shape. One problem withthis is that the two drums must be synchronized for proper operation.

Other problems inherent in existing drip irrigation tapes are that thedrip outlets often become blocked with plant roots growing over or intothem, for example, and that although winding secondary conduits haveadvantages over straight conduits, they are very difficult to make.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a new and improved dripirrigation tape and method of manufacturing such tape.

According to one aspect of the present invention, a drip irrigation tapeis provided which comprises a strip of thin, flexible material having anindented, continuous or segmented groove in one side edge extendinglengthwise along the strip. The other side edge portion is foldedlengthwise along the strip to cover the groove, and the two opposingside edge portions are secured together in face to face contact to forma first or main conduit within the folded strip and a secondary conduitalong the or each groove. Inlets are provided between the main conduitand the or each secondary conduit, and outlets are provided between thesecondary conduit or each secondary conduit segment and the exterior ofthe tape. The groove or each groove segment is shaped to form a windingflow path for water flowing along the secondary conduit, and comprises aseries of oblong chambers interconnected by orifices of smallerdimensions than the chambers, with the chambers alternating in positionfrom one side to the other side of the groove to form a serpentine orwinding passageway. The chambers have opposite end walls which arerounded or radiused in opposite directions from one chamber to the next,to introduce a vortex or swirling, circular motion into the water flow,reducing the flow rate, increasing the water flow path and allowing theconduit to be made of larger dimensions. The swirling, turbulent motionwill also tend to keep any debris moving along the conduit withoutblocking the flow path.

This arrangement of chambers and oppositely radiused end walls insuccessive chambers tends to direct water flow in opposite directions insuccessive chambers along the length of the conduit, producingturbulent, vortex flow conditions tending to reduce the water flow rate.This produces enhanced pressure compensation for variations in waterpressure along the length or run of the conduit. The channel shape alsoacts to help dislodge any debris, since any debris blocking thesecondary conduit will block flow, causing a large pressure back uptending to push debris along the system. The turbulent flow conditionswill also tend to dislodge any debris.

This tape can be laid in much longer runs than was previously possible,and it has been found that a run of 1320 feet will have an 84%coefficient of uniformity along its length. Thus, the length ofirrigation tape which can be laid has been more or less doubled with thetape of this invention.

Preferably, the outlets have raised annular rims projecting radiallyoutwardly from the tubing. The raised outlets act as root deflectors,reducing the risk of roots growing over and into the outlets. Also, thestrip preferably has a wall portion of reduced thickness as compared tothe wall thickness of the remainder of the strip. This reduced thicknessportion is located in the flat side area which will overlie the groovewhen the strip is folded to form the main conduit. This produces somepressure compensation, since the thinner wall portion will tend to flexinto the groove, reducing its dimensions, with increased water pressurein the main conduit, thus reducing flow rate in the secondary conduit asthe water pressure increases, and automatically increasing the flow rateas the water pressure decreases. The pressure compensation effect can beenhanced by making the channel wider and shallower, so that a slightflexing of the wall will produce a relatively large change in thechannel cross-sectional area.

According to another aspect of the present invention, an apparatus forforming the drip irrigation tape is provided, which comprises anextruder for extruding a strip of flexible material, a rotatable shapingdrum having an inwardly extending, continuous or segmented channelextending around its periphery with a serpentine shape matching that ofthe groove to be formed in the strip, a guide for guiding the extrudedstrip around part of the periphery of the drum with a first side edgeportion overlying the channel, the channel having a plurality of spacedsuction ports extending along its length, and a vacuum source connectedto the suction ports via passageways within the drum to pull the sideedge portion overlying the channel into the channel to form a groove ofcorresponding shape in the strip, some of the suction ports being oflarger dimensions than others so that the suction at the larger ports issufficient to pull a raised hole in the strip at that point, the raisedhole forming an outlet from the tape. A folding mechanism is provideddownstream of the shaping drum to fold the strip lengthwise with thefirst side edge portion and an opposite, second side edge portionoverlapping to form a first conduit, and a sealing mechanism is providedfor joining the first and second side edge portions together on oppositesides of the groove to form a seam in which the groove defines asecondary conduit.

Preferably, the guide for guiding strip around the drum includes anopposing drum having a projecting annular rib overlying a portion of thesecond side edge of the strip which will overlie the groove in the firstside edge when the strip is folded. The rib will compress the underlyingstrip material which is still hot and moldable, reducing the strip wallthickness in this region. The thinner material overlying the groove willtend to flex into the groove by an amount dependent on the waterpressure in the first conduit, producing pressure compensation.

According to another preferred aspect of the invention, the connectionbetween the drum and the vacuum source includes a sealing mechanismdesigned to direct the vacuum only to those regions of the drum channelover which the tape extends. This avoids any loss of vacuum pressure asa result of vacuum being directed to vacuum ports elsewhere on the drumwhich are exposed to atmospheric pressure, and provides an increasedvacuum pulling force allowing the strip to be pulled more precisely intothe forming channel. This allows a standard vacuum pump to be used toform a serpentine or tortuous groove on a single shaping drum, avoidingthe need for opposing shaping mandrels which have to be preciselymatched and synchronized.

The drip irrigation tape and forming method and apparatus of thisinvention provides a convenient and relatively inexpensive way of makingserpentine flow conduits to reduce flow rate, allowing the secondaryconduit to be made of larger dimensions and providing improved drip rateuniformity over long runs of the tape. The increased vacuum makes thesecondary conduit straighter and more uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the followingdetailed description of a preferred embodiment, taken in conjunctionwith the accompanying drawings, in which like reference numerals referto like parts, and in which:

FIG. 1 is a side elevation view of an apparatus for forming dripirrigation tape according to a preferred embodiment of the presentinvention;

FIG. 2 is an enlarged top plan view of the shaping drum on the lines2--2 of FIG. 1;

FIG. 3 is an enlarged top plan view of the sealing assembly;

FIG. 4 is a section of the shaping assembly on the lines 4--4 of FIG. 1;

FIG. 5 is an enlarged section on the lines 5--5 of FIG. 4;

FIG. 6 is an enlarged sectional view taken on lines 6--6 of FIG. 1;

FIG. 7 is a sectional view taken on lines 7--7 of FIG. 3;

FIG. 8 is an enlarged detail of part of the side edge portion of thestrip illustrating the preformed edge portion prior to folding;

FIG. 9 illustrates the folding of the flexible strip to form tubing;

FIG. 10 is a section on the lines 10--10 of FIG. 9;

FIG. 11 is a top plan view of a portion of the formed tubing;

FIG. 12 is an expanded plan view of part of the secondary conduit inFIG. 11 illustrating the swirling motion of water along the conduit;

FIG. 13 is a section on the lines 13--13 of FIG. 11.

FIG. 14 is a section similar to FIG. 13 illustrating the effect ofincreased water pressure in the main conduit;

FIG. 15 is a sectional view similar to FIG. 12 illustrating a secondaryconduit with modified dimensions for enhanced pressure compensation;

FIG. 16 is a section on the lines 16--16 of FIG. 11.

FIG. 17 is a view similar to FIG. 11 illustrating a modification;

FIG. 18 is a top plan view of tubing according to another embodiment ofthe invention;

FIG. 19 is a top plan view of irrigation tubing according to anotherembodiment of the invention;

FIG. 20 is a sectional view on the lines 20--20 of FIG. 19;

FIG. 21 illustrates tubing according to another modified embodiment ofthe invention;

FIG. 22 illustrates another alternative embodiment of the invention;

FIG. 23 is a view similar to FIG. 19 illustrating an alternativeconduit;

FIG. 24 is a similar view illustrating a short emitter configuration;

FIG. 25 is an enlargement of a portion of the conduit of FIG. 23;

FIG. 26 is a sectional view taken on line 26--26 of FIG. 25;

FIG. 27 is a sectional view taken on lines 27--27 of FIG. 25;

FIG. 28 is a view similar to FIG. 25 illustrating an alternative bafflearrangement;

FIG. 29 is a sectional view taken on line 29--29 of FIG. 28;

FIG. 30 is a top plan view showing a further outlet configuration;

FIG. 31 is an enlarged sectional view taken on line 31--31 of FIG. 30;and

FIG. 32 is a sectional view taken on line 32--32 of FIG. 31.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-11 of the drawings illustrate an apparatus and method forforming a drip irrigation tape 10 according to a first embodiment of thepresent invention. The formed tape as illustrated in FIGS. 11-13basically comprises a strip of thin, flexible, water impervious materialsuch as polyethylene or silicone rubber, with a series of spaced,indented grooves 14 of generally serpentine shape formed along one sideedge 16 of the strip, the opposite side edges 16 and 18 of the stripbeing folded into overlapping relationship and sealed together to form amain conduit 20 along the length of the strip and a series of spaced,secondary conduit segments 22 along each of the grooves 14. Inlets 126are provided between the main conduit and the inlet end 24 of eachsecondary conduit segment 22, while outlet ports 25 having raised rims26 are formed between each secondary conduit and the exterior of thetape.

In the preferred embodiment illustrated, the groove is discontinuous andcomprises a series of spaced groove segments. However, it will beunderstood that the tape may alternatively be formed with a continuousgroove of similar shape, having spaced inlets and outlets along itslength for connecting the main conduit to the secondary conduit and thesecondary conduit to the exterior of the tape.

A preferred embodiment of an apparatus for making the tape isillustrated in FIGS. 1-7, while FIGS. 8-10 illustrate stages in themanufacture. The apparatus includes an extruder 28 for extruding a strip30 of material for forming the tape, and a shaping station 32 at whichthe grooves 14 are formed in side edge 16 of the strip while it is stillmolten from the extrusion process. A folding mechanism 34 is locateddownstream of the shaping station 32 for folding the strip with itsopposite side edges overlapping, followed by heat sealing station 36 forsealing the overlapping side edges together to form the separate mainconduit and secondary conduit segments. After the heat sealing station,the formed tape is passed over a series of guide rollers and coolingwheels 38 before being wound onto a storage spool 40.

As illustrated in FIG. 1, the various parts of the apparatus between theextruder and storage spool are supported on a frame or back plate 42within a suitable outer housing (not illustrated). The extruder is of aknown type for forming thin polyethylene or similar material film orstrip, and includes a hopper 44 into which suitable raw material such aspolyethylene beads are placed, and an extrusion die 46 through which athin film of molten plastics material is forced. The die has a slotdesigned to form strip having a thickness in the range of around 0.005to 0.02 inches (5 to 20 mils.). Preferably, the slot has an enlarged orthickened region to form a bulge in the extruded strip, at the areawhere the channel or groove is to be formed. This allows the wallthickness of the formed groove to be made thicker than the remainder ofthe strip, for example it may be 2 mil. greater than the remainder ofthe strip and may be up to 10 mil. thicker. However, in somearrangements the wall thickness may be uniform over the entire strip,including the groove.

The shaping station assembly is best illustrated in FIGS. 2, 4 and 5,and comprises a shaping drum 48 rotatably mounted via axle 50 on backplate 42, and an opposing, rotatably mounted guide drum 52 for guidingand compressing the still molten strip onto the shaping drum 48. Strip30 arriving at drum 48 will still be at a temperature of around 400degrees Fahrenheit from the preceding extrusion step. As illustrated inFIG. 2, the drum 48 has a series of indented channels 53 extendingaround its periphery adjacent one side edge of the drum. The shape ofthe channels 53 corresponds to the desired shape of the secondaryconduit segments 22 in the formed strip, and as illustrated in FIG. 2each channel is of generally serpentine or zig-zag shape with a V-shapedportion 54 intersecting one end of each channel 53.

As best illustrated in FIGS. 4 and 5, the drum 48 has a hollow interior55 between spaced front and back walls 56 and 58. Axle 50 projects fromback wall 58 through a bearing 60 in back plate 42. An inlet tube 62extending through axle 50 and back plate 58 connects the drum to asuitable vacuum source such as a vacuum pump. A dividing wall or plate64 in the drum separates the vacuum inlet from the interior 55 of thedrum. Each channel 53 has a series of suction ports 66 extending alongits length, with one of the ports 68 at one end of the channel being oflarger dimensions than the remaining ports. The ports 66, 68 are allconnected via circumferential passageways 70 underlying each channel andradial passageways 72 formed in dividing wall 64 to a central chamber 74in dividing wall 64. Vacuum inlet 62 extends through seal member 76 intothe central region 74 of the plate. The seal member 76 has an enlargedhead 78 at its inner end which is a close fit in chamber 74, as bestillustrated in FIG. 5, with a segmental shaped cut-out 80 formed in head78 to direct the vacuum only into some of the radial passageways 72 atany one instant of the drum's rotation forming a selective seal. As thedrum rotates in the direction of the arrow in FIG. 5, plate 64 willrotate relative to stationary seal member 76, bringing successivepassageways 72 into alignment with cut-out region 80 of the seal. Thisarrangement is such that the vacuum is directed only to those portionsof the drum over which the strip is guided, and is therefore not exposedto the atmosphere through any of the uncovered suction ports. Thisallows the vacuum force to be concentrated in the regions where it isneeded in order to suck the strip material into the underlying channelsand form the shaped grooves. As the drum rotates in the direction of thearrow in FIG. 5, successive passageways will become aligned with cut-out80 just as the strip 30 starts to travel over the channel connected tothose passages, as best illustrated in FIG. 5, so that the vacuum isconnected to the suction ports around the region of the drum illustratedin FIG. 5 only.

The force of the vacuum pulling the molten strip material into thechannels will be sufficient to form grooves of corresponding shape tothe channels along the side edge 16 of the strip. The larger suctionports 68 apply sufficient suction to pull holes in the strip material atone end of each channel, forming the outlet ports 25 with raised rims26, which are best illustrated in FIG. 13. The drum is also connectedvia a rotary coupling 82 in the front wall to water inlet and outlethoses 84, 86, which supply cooling water to the interior of the drum,cooling the strip as the grooves are formed.

As best illustrated in FIG. 4, the drum 52 has an annular, projectingrib 88 adjacent the opposite side edge to the channels 53 in drum 48.This compresses the underlying strip material to reduce the wallthickness in that region 90, as can be seen in FIG. 4. Alternatively,the drum may have a groove in this region to increase the wall thicknessin the region 90, if desired, as will be explained in more detail below.In other arrangements, the wall thickness may be uniform over the entirestrip including the groove.

FIG. 8 illustrates a portion of the strip preformed with grooves 14 asit leaves the shaping drum. As the strip leaves drum 48, it is passedover several guide rollers 92 and into folding mechanism 34. The foldingmechanism is of a known type and folds the strip lengthwise as generallyillustrated in FIG. 9, so that the opposite side edge portions areoverlapped with the first portion 16 having the indented grooves on theoutside and the second portion 18 covering the grooves on the inside ofthe tubing, the thinner wall thickness region 90 being aligned with thegrooves, as illustrated in FIG. 10, which illustrates the form of thetubing as it leaves the folding mechanism and is guided onto heatsealing drum 94 at the heat sealing station 36.

As best illustrated in FIGS. 3, 6 and 7 heat sealing drum 94 isrotatably mounted on back plate 42 via axle 95, and includes a recessedportion 96 separating the drum into a front portion 98 and a backportion 100. A brass heat sealing wheel 102 having raised annular ribs104, 106 extending along its opposite edges is set into recessed portion96 of the heat sealing drum 94. Inclined transverse ribs 108 extendbetween the annular ribs at spaced intervals corresponding to the gapsbetween adjacent grooves in the formed tubing. Flat spots or gaps 110are formed in the rib 104 adjacent each transverse rib 108. The heatsealing wheel 102 is heated via a suitable electrical heatingarrangement, as best illustrated in FIG. 7. Suitable means such ascommutator rings 112 and contacts 114 serve to couple an external powersupply (not shown) to a junction box 116, from which it is coupled toelectrical cartridge resistors 117 attached to the heat sealing wheel.

The shaping drum and heat sealing drum are rotated in synchronism by asuitable drive mechanism. As the folded strip passes around the heatsealing drum, the grooved portion will overlie the recessed portion ofthe drum, as illustrated in FIG. 6. The strip is pressed against theheat sealing wheel by a pressure belt assembly 118, and the raised ribsapply pressure to the overlapped portions of the strip, at the same timeheating the strip to melt the strip material and form heat seal lines120, 122 extending along opposite sides of the grooves and spacedoutwardly from the grooves, as best illustrated in FIG. 11. Flat orrecessed spots 110 along rib 106 separate the rib from the stripmaterial in this region to produce breaks or gaps 124 in one of the seallines 120, and these gaps are aligned with the V-shaped portions orinlets 126 at the end of each groove formed by the correspondingV-shaped portion of the shaping drum. This produces a break in the seamor an inlet 24 connecting the interior of the tube, or the main conduit20, to each secondary conduit 22.

The transverse ribs form a corresponding transverse seal line 128between heat seal lines 120, 122 between each adjacent pair of groovesor secondary conduits 22, separating the secondary conduits from eachother. After leaving the sealing station 36, the formed tape is guidedaround guide rollers and cooling wheels 38 before being wound onto thestorage spool 40 at the outlet of the apparatus.

Since the overlapping side edge portions of the tape are sealed togetherin face to face contact with no intervening material between theoverlapping portions along the seal lines, the depth of groove controlsthe dimensions of the secondary conduit, and allows the dimensions, andthus the flow rate, to be relatively constant along the length of thetape.

The finished irrigation tape or tubing may be cut to any desired lengthand laid on or in the ground in a region to be irrigated with one endconnected to a water supply. Water supplied at one end will flow alongthe main conduit 20 within the tubing, and will communicate via inlets24 with each secondary conduit 22. Water flowing along the tortuous,serpentine secondary conduits 22 will trickle at a relatively slow andconstant rate out of raised outlets 25. The raised rim 26 of outlets 25will tend to deflect any roots or other debris which may otherwise growover or into the outlets, potentially blocking the outlets from somesecondary conduits and producing irregular irrigation. Although only oneoutlet 25 is illustrated at the end of each secondary conduit, two ormore outlets may be provided so that the flow is not cut off if one ofthe outlets should become blocked.

The shape of the serpentine groove is best illustrated in FIGS. 11 and12. The groove is shaped to form a series of elongate chambers 130offset alternately on opposite sides of the grooved region andinterconnected by orifices 132 of reduced dimensions between adjacentends of each pair of chambers. The ends 134 of the chambers are roundedor radiused, and the ends of adjacent chambers overlap one another toform a generally S- or Z-shaped path between adjacent chambers, asillustrated by the arrows in FIG. 12 between two adjacent chambers. Theradiused ends introduce a swirling, circular or vortex-type of flowpattern in water at each end of each chamber 130, increasing the flowpath and reducing the flow rate. The water flow will change directionfrom one chamber to the next, from a clockwise to an anti-clockwisegenerally circular motion, as illustrated by the arrows in FIG. 12. Thisswirling flow will reduce the flow rate along the conduit, allowing theconduit dimensions to be made larger for a predetermined drip rate andthus reducing the risk of debris blocking the conduit. The swirling,vortex-type flow also produces a better pressure drop. The swirlingliquid motion will also tend to keep any debris moving along theconduit, reducing the risk of debris accumulating to block the flow.

Preferably, the wall thickness of the portion 90 of the side edge whichoverlies conduits 22 is reduced, as illustrated in FIGS. 13 and 14. Thewall thickness of the tubing will generally be in the range of 5 to 15mil., and can go up to 20 mil. which is used in some segment of themarket around the periphery of the main conduit, with the groove itselfhaving the same or greater thickness of the order of 0 to 10 mil. overthe remainder of the wall, as mentioned above. Preferably, the reducedthickness region 90 will have a wall thickness of the order of 5 to 8mil. and may go up to 10 mil. This reduced thickness combined with theoverall flexibility and memory of the polyethylene material forming thetubing allows region 90 to flex into the secondary conduit both alonginlets 126 and along the length of the secondary conduit segment 22 asthe pressure in the main conduit 20 increases. This effect isillustrated in FIG. 14. The reduced thickness region 90 will tend tobulge inwardly into the secondary conduit under increased fluid pressureP in the main conduit, reducing the dimensions and thus the flow rate inthe secondary conduit. When the pressure is reduced, the region 90 willrelax back outwardly to increase the secondary conduit dimensions.Alternatively, where less stretching is required, for example underhigher flow conditions, region 90 may be made thicker than the remainderof the tubing.

In one example, say the total pressure on the inner side of wall 90 is csquare inches×6 p.s.i. where c is the surface area. If c is 10 squareinches then the pressure is 6×10 or 60 pounds. If the pressure on theother side of wall 90, within the secondary conduit, is 0.5 p.s.i., say,the pressure is 10 square inches×0.5 or 5 pounds so the net outwardpressure on wall 90 is 60-5 or 55 pounds (5.5 pounds per square inch).The pressure on the outer wall of secondary conduit 22 is about 12square inches×0.5 or 6 pounds. The pressure on inner wall 90 is thus 12times that on the outer wall of the secondary conduit. This however, isnot entirely controlled by the respective thickness of the inner andouter walls. The pressure is controlled by the strength of section 12against stretching and the incompressible liquid in outer channel 22.However by making wall region 90 sufficiently thin, it can stretch more,allowing more of the water pressure in the main conduit to be exerted onthe secondary conduit, producing improved pressure compensation.

This arrangement allows the dimensions of the secondary conduit to bevaried to a certain extent dependent on water pressure in the mainconduit. This produces some compensation for variations in waterpressure which would otherwise cause major variations in the drip rate.When the water pressure in the tubing goes up, the thin wall region willtend to flex inwardly into the channel, reducing the dimensions of thesecondary conduit and thus reducing the flow rate along the secondaryconduit and ultimately the drip rate. The inlet passageway dimensionswill also be reduced. As the water pressure goes down, the region willrelax outwardly and increase the secondary conduit dimensions. Thisallows a much more uniform drip rate to be achieved along relativelylong runs of tape.

This pressure compensation effect can be increased with the modificationillustrated in FIG. 15. In this embodiment, the secondary conduit 222 ismade wider and shallower than in FIGS. 13 and 14, although it preferablyhas the same basic serpentine shape as illustrated in FIG. 12.Additionally, the groove 214 is completely rounded or radiused incross-section, with no square corners as in FIGS. 6 or 13. This can beachieved by suitably machining the channels 53 in the shaping drum toform rounded or radiused channels, so that the channel is arcuate incross section along its length. As in the version of FIGS. 13 and 14,the inner wall section 290 of the conduit is thinner than that of theremainder of the wall surrounding main conduit 220, and will thereforetend to bulge under increased fluid pressure. This will reduce thedimensions of secondary conduit 222, as indicated in dotted outline inFIG. 15. The secondary conduit may have a depth of the order of 0.003 to0.004 inches and a width of up to 0.1 inch, for example, in thisversion, to produce a very sensitive pressure compensation. With thisarrangement, only a very slight flexing of region 290 will produce arelatively large difference in the cross-sectional area of conduit 222,thus reducing the flow rate as the pressure increases and compensatingfor pressure variations along the length of the tubing.

With this tubing, the vortex turbulent flow in the secondary conduitallows the grooves to be of larger dimensions and the secondary conduitto be shorter while still maintaining a relatively low flow rate. Thedepth of the grooves may be of the order of 10 to 30 mils., for example,with the chambers 130 having a width of up to 100 mils. The increasedvacuum force directed only to the region of the drum where it is neededforms the grooves accurately and precisely matching the channels in theshaping drum. The enlarged secondary conduit dimensions combined withthe flow characteristics of the serpentine groove substantially reducethe risk of debris blocking any secondary conduit. This permits longerruns of tubing to be used, with lengths of up to 1320 feet being foundto have around 84% or better coefficient of uniformity. Thus, muchlarger areas can be covered with a single run of tubing than waspreviously possible without loss of uniformity in the drip rate andcorresponding lack of uniformity in the crop. The elongate flow chambers130 combined with the swirling, vortex flow allow more time for pressurecompensation to take effect. In a laminar flow secondary conduit, theoutlet flow rate will more or less double if the water pressure doubles.With secondary conduits of the shape illustrated in FIGS. 11 and 12, adoubling in the water pressure increases output flow only 50%.

FIG. 17 illustrates a modification to the seal arrangement in the tubingof the previous embodiments. The tubing of FIG. 17 is otherwiseidentical to that of the first embodiment and like reference numeralshave been used where appropriate. In the modified version of FIG. 17, anadditional seal region 121 is provided transversely between the legs ofthe V-shaped inlet grooves 126 and in alignment with one of the seallines 120. The seal region 121 has tapered or inclined ends which matchthe taper of the respective adjacent inlet channels 126, as illustratedin FIG. 7. Additionally, seal lines 120 and 122 have enlarged, opposingseal regions 123, 125 which extend inwardly up to the opposite sides ofthe secondary conduit or groove 22 adjacent the inlet end of eachsecondary conduit segment. These additional seal regions 121, 123 and125 may be formed by suitable modification of heat sealing ribs on theheat sealing drum 94.

With these additional seal areas at the inlet end of each secondaryconduit segment, any tendency for the overlapping side edge portions ofthe strip to spread apart at the inlet and allow additional water toflow into the secondary conduit is eliminated, since these edge portionsare positively sealed together. With the arrangement of FIG. 11, theremay be some tendency for the overlapping regions of the strip toseparate under high pressure conditions, particularly between theV-shaped inlet channels 126, to form a bridge and allow a greater flowrate of water into the secondary conduit. The additional seal regions inFIG. 17 will avoid this possibility.

Drip irrigation tape is typically provided in a range of standard outletspacings, dependent on grower's requirements This range is 8", 12", 16"and 24" outlet spacings. For each outlet spacing, the secondary conduitwill be dimensioned and designed to produce a predetermined drip rate ingallons per minute per hundred feet of tape, for example 1/10 and 7/10gallons per minute. Clearly, if the same secondary conduit is providedbetween outlets for a 12" outlet spacing and a 24" outlet spacing, i.e.with the secondary conduit segment being double the length for the 24"outlet spacing, the drip rate will be lower for the 24" tape than forthe 12" tape. This variation may be avoided either by varying thedimensions of the 24" outlet tape to increase the flow rate, or by usingthe same length secondary conduit in both cases. For example, for theformer alternative, a secondary conduit shaped and dimensioned toprovide 4/10 gal/min/100 feet in a 12" outlet spacing will provideapproximately 2/10 gal/min/100 feet in a 24" outlet spacing tape. Thelatter alternative of using the same length secondary conduit segmentfor every outlet spacing is illustrated in FIG. 18. The shape of thesecondary conduit segments 22 and other components of FIG. 18 areequivalent to the embodiment illustrated in FIG. 11, and like referencenumerals have been used where appropriate.

In FIG. 18, the spacing between outlets 25 is twice that of the versionof FIG. 11, but each secondary conduit segment 22 has the same length asin FIG. 11, with a region 310 between adjacent conduit segments 22 beingblanked or sealed off by transverse seal lines 312 extending betweenseal lines 120 and 122. The configuration of the secondary conduitsegments 22 is identical to that of FIG. 11, in which the conduitsegments extend for substantially the entire length between adjacentoutlets.

In practice, any suitable secondary conduit length may be selected foruse with all outlet spacings, from 1" upwards, with the region betweenadjacent segments simply being blanked off. This allows the outlet flowrate to be controlled more easily for any outlet spacing. The advantageof using a standard secondary conduit length is that design expense isreduced, since the same variation in secondary conduit dimensions willproduce the same change in flow rate for any outlet spacing. However,there are also some benefits in running the secondary conduit segmentfor the entire length between adjacent outlets, for example this permitsthe secondary conduit to be made larger since the flow rate is reducedby providing a longer flow path to the outlet, at the same time reducingthe risk of clogging and providing more scope for pressure compensation.

Tape may be manufactured in a range of different outlet spacings, eitherwith secondary conduits segments extending between outlets or withappropriate blanked off regions as in FIG. 18, simply by providing anequivalent range of shaping drums 48 with appropriately shaped channels53, with or without blanked off regions between adjacent channels.

FIGS. 19 and 20 illustrate another embodiment of the invention in whichdrip irrigation tape 350 is formed in the same manner as tape 10 in FIG.11 but the secondary conduit segments 352 are each formed with aserpentine or winding portion 354 extending from inlet channels 356 inwhich water is directed back and forth, and a second, pressurecompensating section 358 extending from winding portion 354 to raisedoutlet 360, which is equivalent to raised outlet 25 in the firstembodiment.

As in the first embodiment, the tape is made by first forming a seriesof indented groove segments along one side edge of the tape in theappropriate shape for forming the secondary conduit segments, and thenfolding the tape with the side edges overlapped before sealing themtogether along spaced seal lines 362, 364, with transverse seal lines365 extending between the seal lines to separate adjacent secondaryconduit segments, and gaps 366 in the seal line 362 at each V-shapedinlet channel. The pressure compensating section 358 comprises astraight groove, with a series of indented steps 368 in its base formingbarriers in the channel for directing water in an up and down direction,as best illustrated in FIG. 20, rather than transversely back and forth.This stepped section forms successive small size orifices 370 andenlarged pressure relieving chambers 372. As in the previousembodiments, the opposing flat side edge portion 374 of the tape isformed with a reduced thickness wall portion opposing the groove in theopposite side edge portion, as can be seen in FIG. 20.

With this arrangement, as the pressure inside the main conduitincreases, the reduced thickness portion of wall 374 will tend to bulgeoutwardly towards indented steps 368, reducing flow towards the outletby an amount substantially proportional to the increase in pressure. Atthe same time, the water is directed up and down to follow the steppedconfiguration of the secondary conduit, introducing up and downturbulence and similarly reducing and controlling flow. Thus, anequivalent outlet flow rate can be produced for a secondary conduit oflarger dimensions than an equivalent laminar flow secondary conduit. Ifthe pressure compensating section should become blocked by debris at anyof the small orifices 370, back up pressure will force the opposingsurfaces of the conduit apart and push the debris into the next adjacentpressure relieving chamber 372.

FIG. 21 illustrates a modification in which the entire secondary conduitsegment 380 is of the same shape as the pressure compensating section atthe outlet end in FIG. 19, while FIG. 22 illustrates an embodiment inwhich a pressure compensating section 382 is provided at the inlet endof a secondary conduit segment while the remainder 384 of the secondaryconduit segment is of equivalent shape to the inlet section in FIG. 19.In both FIGS. 21 and 22, like reference numerals to FIG. 19 have beenused for like parts. Both of these alternative versions will produceturbulent, up and down flow along at least part of the length of eachsecondary conduit segment with improved pressure compensation via thegradual closing of the small orifices between adjacent pressurerelieving chambers as the pressure within the main conduit rises. Thisarrangement has been found to provide good pressure compensation withlittle variation in the output flow rate as pressure increases withinthe tubing.

The stepped groove is formed by a shaping wheel equivalent to shapingwheel 48 but having channels with a similar stepped formation along partor all of their length.

FIG. 23 illustrates another modification in which the entire secondaryconduit segment 390 is of winding or serpentine shape, as in the firstembodiment, and pressure compensating barriers 392 are formed in each ofthe chambers 394 between adjacent turns 396 of the winding channel.Although in the illustrated embodiment the pressure compensatingbarriers are provided along the entire length of the secondary conduit,the pressure compensating region may alternatively extend only part ofthe length of the secondary conduit, for example adjacent the outlet asin FIG. 19 or adjacent the inlet as in FIG. 22 or anywhere else in theconduit. Only one inlet channel 395 is provided at the inlet end of thesecondary conduit. The inlet may be deeper than the rest of the conduit.This version may alternatively have two inlets as in the otherembodiments, and the other embodiments may alternatively have only oneinlet as illustrated in FIG. 23 instead of two inlets. The dripirrigation tape in this embodiment is otherwise identical to that ofFIG. 19. Like reference numerals have been used as appropriate. Thebarriers 392 are illustrated in more detail in FIGS. 25 to 27, and areformed by a series of indented steps 398 formed in the grooved side edgeportion of the tape, one step being formed at the center of each chamber394. Preferably the steps are of rounded, generally arcuate shapes, asillustrated in FIG. 27, although other shapes such as, rectangular orelliptical may be used, and the height of the step may be varied to suitthe particular application. As in the previous embodiments of FIGS.19-22, the steps may be formed by an equivalent stepped formation in theshaping wheel forming the serpentine groove.

The steps or barriers 392 form a series of successive small sizeorifices 399 and enlarged pressure relieving chambers in the secondaryconduit. As in the embodiment of FIG. 19, this will tend to reduce theflow rate in a pressure compensating manner, since the small orificeswill gradually close more and more with increase in pressure within themain conduit. The overall effect will be a relatively constant outputflow rate regardless of variations in the water pressure in the tubing.

FIGS. 28 and 29 illustrate an alternative pressure compensatingarrangement in which barriers 400 are provided in the turns or bends 402of the serpentine passageway rather than in the chambers betweenadjacent turns as in FIG. 23. The drip irrigation tape in thisalternative will be otherwise identical to that of FIG. 23. As bestillustrated in FIG. 28, the barriers 400 are formed by constrictions orsteps 402 at the base of the groove formed in one side edge portion ofthe tape, but the steps in this case are located at turns in theserpentine groove to form a reduced size orifice 404 at each bend orturn between adjacent enlarged chambers 406 in the passageway. Again,this will tend to compensate for any pressure variations to produce asubstantially constant output flow rate.

FIG. 24 illustrates another alternative embodiment of the inventionwhich is similar to the embodiment of FIG. 18, and like referencenumerals have been used where appropriate. As in FIG. 18, shortsecondary conduit segments 410 are provided, which are significantlyshorter than the distance between adjacent outlets 25. However, unlikeFIG. 18, the conduit segments 410 are straight and have a series ofspaced barriers or steps 412 along their length as in the embodiment ofFIG. 21, in order to produce a turbulent, up and down flow along thelength of each segment 410. The barriers form small orifices betweenadjacent pressure relieving chambers 414, and the orifices will tend toclose gradually as pressure within the main conduit increases, reducingflow rate with increased pressure to produce little variation in outputflow rate as pressure within the tubing changes. As in FIG. 18, theregion 310 between adjacent conduit segments 410 is blanked or sealedoff by transverse seal lines 312 extending between seal lines 120 and122.

FIGS. 30-32 illustrate a modified outlet 510 which may replace theoutlet ports 25 of any of the previous embodiments. The outlet 510 isillustrated in FIGS. 30-32 at the end of a conduit segment of the typeillustrated in FIG. 11, and like reference numerals have been used whereappropriate. However, it will be understood that such an outlet may beused in any of the previous embodiments, as noted above. Also asillustrated in FIG. 30, the inlets 126 are replaced with modified inlets520. In alternative arrangements, the inlets in FIG. 30 may be of theform illustrated at 126 in the previous embodiment.

The outlet 510 comprises an outlet chamber 512 at the outlet end of aconduit segment 22 which is similar to chambers 130 but is both widerand deeper than the remaining chambers. The chamber 512 has a linearslit 514 cut in its top wall 516, as best illustrated in FIG. 32. Slit514 may be laser cut.

Preferably, the depth of chambers 130 is of the order of 0.018 to 0.028inches while the depth of the outlet chamber 512 is in the range from0.030 to 0.060 inches. The length of the outlet chamber is approximatelythe same as that of the remaining chambers, and is preferably in therange of 0.120 to 0.160 inches, while the length of the slit 514 isaround 0.120 inches in a chamber of length 0.160 inches. The width ofthe outlet chamber is preferably in the range from 0.010 to 0.050inches.

With this arrangement, the slit or outlet 514 will tend to remain closedwhen no water is flowing through the device, so that roots cannot growinto the outlet and block it. When water fills the outlet chamber 512,the slit will be forced open with the opposite sides forced slightlyupwardly, also acting as root deflectors. This outlet is of simplerconstruction than the previous embodiments, since no raised rim isrequired, but still has the desired effect of deflecting roots fromgrowing into the outlet.

The inlets 520 also comprise an inlet chamber 522 at the inlet end ofconduit segment 22 which is of the same width as outlet chamber 512. Thechamber 522 has two linear outlet slits 524 laser cut in its bottomwall, i.e. in the side edge 18 of the tape underlying chamber 522.Inlets 524 will also tend to open inwardly on exposure to fluid pressureinside the hose.

Although a preferred embodiment of the present invention has beendescribed above by way of example only, it will be understood by thoseskilled in the field that modifications may be made to the disclosedembodiment without departing from the scope of the invention, which isdefined by the appended claims.

I claim:
 1. A drip irrigation tape, comprising:a strip of flexiblematerial having at least one indented groove in one side edge extendinglengthwise along the strip, the opposite side edge being foldedlengthwise along the strip to cover the groove; the opposing side edgesof the strip being secured together in face to face contact alongopposite sides of the groove to form a main conduit within the foldedstrip and at least one secondary conduit along the groove; the striphaving at least one inlet connecting the main conduit to the or eachsecondary conduit, and at least one outlet connecting the or eachsecondary conduit: to the exterior of the tape; the groove having agenerally serpentine shape extending along a grooved region, the groovecomprising a series of elongated chambers offset alternately on oppositesides of the grooved region, each pair of adjacent chambers beinginterconnected by a connecting orifice of smaller dimensions than thechambers at adjacent ends of the respective chambers, at least the endwalls of the chambers being rounded to introduce circular directionalmotion into water flowing through the chambers; and the wall thicknessof a portion of the side edge covering the groove being less than thethickness of the remainder of the strip.
 2. The tape as claimed in claim1, wherein adjacent chambers have overlapping ends and each connectingorifice forms a generally S-shaped connection between the chambers, theS-shaped connections being oppositely directed at opposite ends of eachchamber to reverse the water flow direction.
 3. The tape as claimed inclaim 1, wherein a series of spaced, segmented grooves are formed alongthe length of the strip to form a series of spaced secondary conduits,each secondary conduit having at least one inlet at one end and oneoutlet at the opposite end.
 4. The tape as claimed in claim 3, whereineach secondary conduit includes a pressure compensating region extendingalong at least part of its length, the pressure compensating regionhaving a stepped wall forming a series of barriers in said secondaryconduit defining successive small orifices and enlarged pressurerelieving chambers between adjacent orifices.
 5. The tape as claimed inclaim 4, wherein the pressure compensating region extends up to theoutlet end of each secondary conduit.
 6. The tape as claimed in claim 4,wherein the pressure compensating region extends from the inlet end ofeach secondary conduit.
 7. The tape as claimed in claim 4, wherein thepressure compensating region extends the entire length of the secondaryconduit.
 8. The tape as claimed in claim 4, wherein the pressurecompensating region comprises at least part of the length of saidserpentine groove.
 9. The tape as claimed in claim 8, wherein saidstepped wall forms at least one barrier in each of said elongatedchambers.
 10. The tape as claimed in claim 8, wherein said stepped wallforms a barrier at the junction between each pair of adjacent chambers.11. The tape as claimed in claim 1, wherein the wall thickness of thegroove is greater than that of the remainder of the strip.
 12. The tapeas claimed in claim 11, wherein the groove has a wall thickness between2 and 10 mil. thicker than the remainder of the strip.
 13. The tape asclaimed in claim 1, wherein the wall thickness of said portion overlyingthe groove is between 5 to 8 mil.
 14. The tape as claimed in claim 1,wherein the or each inlet comprises a V-shaped groove intersecting oneend of said serpentine groove at the apex of the V-shape to form a pairof inlet channels converging towards one another, and the opposing sideedges of the strip are sealed together in the region between the inletchannels of each V-shaped inlet.
 15. The tape as claimed in claim 1,wherein the chambers comprise pressure compensating chambers and have awidth greater than their depth.
 16. The tape as claimed in claim 1,wherein the groove is arcuate in transverse cross section.
 17. A dripirrigation tape, comprising:a strip of flexible material having a seriesof spaced, segmented grooves in one side edge extending lengthwise alongthe strip, the opposite side edge being folded lengthwise along thestrip to cover the grooves; the opposite side edges of the strip beingsecured together in face to face contact along opposite sides of thegrooves to form a main conduit within the folded strip and a series ofspaced secondary conduits along the grooves; each secondary conduithaving at least one inlet at one end connecting the main conduit to eachsecondary conduit, and at least one outlet at the opposite endconnecting each secondary conduit to the exterior of the tape; thegrooves each having a generally serpentine shape extending along agrooved region, each groove comprising a series of elongated chambersoffset alternately on opposite sides of the grooved region, each pair ofadjacent chambers being interconnected by a connecting orifice ofsmaller dimensions than the chambers at adjacent ends of the respectivechambers, at least the end walls of the chambers being rounded tointroduce circular directional motion into water flowing through thechambers; and each outlet comprising an outlet chamber at said oppositeend of each secondary conduit, the outlet chamber having a base wallwith an elongate slit connecting the chamber to the exterior of thetape.
 18. The tape as claimed in claim 17, wherein the outlet chamber isof similar shape to the remainder of the elongated chamber and of largerdimensions.
 19. The tape as claimed in claim 17, wherein the slit islaser cut and extends along a major part of the length of the outletchamber.
 20. The tape as claimed in claim 17, wherein the outlet chamberis wider than the remainder of the chambers.
 21. The tape as claimed inclaim 17, wherein the outlet chamber is deeper than the remainder of thechambers.
 22. A drip irrigation tape, comprising:a strip of flexiblematerial having a series of spaced, segmented grooves in one side edgeextending lengthwise along the strip, the opposite side edge beingfolded lengthwise along the strip to cover the grooves; the oppositeside edges of the strip being secured together in face to face contactalong opposite sides of the grooves to form a main conduit within thefolded strip and a series of spaced secondary conduits along thegrooves; each secondary conduit having at least one inlet at one endconnecting the main conduit to each secondary conduit, and at least oneoutlet at the opposite end connecting each secondary conduit to theexterior of the tape; the grooves each having a generally serpentineshape extending along a grooved region, each groove comprising a seriesof elongated chambers offset alternately on opposite sides of thegrooved region, each pair of adjacent chambers being interconnected by aconnecting orifice of smaller dimensions than the chambers at adjacentends of the respective chambers, at least the end walls of the chambersbeing rounded to introduce circular directional motion into waterflowing through the chambers; and each inlet comprising an inlet chamberat said one end of each secondary conduit, the inlet chamber having alower wall with at least one slit connecting the inlet chamber to themain conduit.